Transfer molding apparatus

ABSTRACT

An apparatus for molding elastomeric stock, comprising an apertured, heat-resistant, flexible, insulation plate between a heated mold and the discharge portion of an elastomeric stock injection unit such that respective mold cavities provided in the mold are aligned with respective apertures in the insulation plate which intercommunicate the mold cavities with an internal discharge chamber in the injection unit. The mold and injection unit are moved relative to one another such that each presses against the other through the intermediary of the insulation plate, thereby permitting expulsion and transferring of a portion of elastomeric stock from the injection unit into the mold cavities to be cured, an excess portion of elastomeric stock remaining in the injection unit being prevented from undergoing curing by means of the presence of the insulation plate.

United States Patent 1 [1 3,859 024 Pasch et al. Jan. 7, 1975 [5TRANSFER MOLDING APPARATUS 3,360,829 1/1968 Germ 425/251 Inventors:Lambert Pasch Nutheim; Heinz 3,392,2l7 7/1968 Zitzloff 425/DlG. 228Aachen both of Primary Examiner-Francis S. Husar ermany AssistantExaminer-David B. Smith [73] Assignee: Uniroyal A.G., Aachen, Germany Arn y, g or FirmPhiliP S E q- [22] Filed: Dec. 18, 1972 [57] ABSTRACT PPN05 316,165 An apparatus for molding elastomeric stock, comprising anapertured, heat-resistant, flexible, insulation [30] Foreign ApplicationPriority Data plate between a heated mold and the discharge por- D 231971 G 264219 tion of an elastomeric stock injection unit such thatermany respective mold cavities provided in the mold are aligned withrespective apertures in the insulation 425/251 4;2 5: 352 plate whichintercommunicate the mold cavities with [58] Fie'ld 228 252 an internaldischarge chamber in the injection unit. 'h X The mold and injectionunit are moved relative to one another such that each presses againstthe other through the intermediary of the insulation plate, [56]References Clted thereby permitting expulsion and transferring of a por-UNITED STATES PATENTS tion of elastomeric stock from the injection unitinto 2,300,759 11/1942 Amigo 425/DIG. 229 X the mold cavities to becured, an excess portion of 2,413,401 12946 Youngblood at 425/145 Xelastomeric stock remaining in the injection unit being IIIIIIIIIIIIprevented fromnndergoing curing by means of the 3 015 131 l/l962 Hehl.1: III: 425/D1GI 222x presence Ofthe msulaton plate 3,121,918 2/1964Jurgeleit 425/190 28 Claims, 9 Drawing Figures FATE sum 2 or 6 NTEUJAN,7-

PATENTEDJAH (I975 3.859.024

' sum 6 or e TRANSFER MOLDING APPARATUS BACKGROUND OF THE INVENTION Thisinvention relates to apparatus for molding parts from viscous materialsand, more particularly, to molding apparatus in which molding compound,or elastomeric stock, is transferred from an injection cylinder to aplurality of closed mold cavities through the intermediary of aplurality of passageways which intercommunicate the cylinder with thecavities.

One example of such a molding apparatus is the invention of Herbert F.Jurgeleit disclosed in U.S. Pat. No. 2,883,704, dated April 28, 1959. Inthis patent a multi-plate, flashless mold is provided having a pluralityof cavities therein. The term flashless mold as used herein hasreference to a multi-cavity, multi-part mold in which the cavity formingportions of the mold are independently movable sufficiently to permitindependent stacking or closing of such portions either by reason of anactual flexure of the flexible plate member which either forms ordirectly supports such portions of the mold, or by reason of a movementof such portions relative to a retainer plate, and in which the forcefor independently closing or holding such cavity forming portions closedis transmitted to each group of cavity forming portions by a commonconformable medium such as the molding compound or other conformablemedium. Each cavity of the flashless mold is closed except for thepresence of a plurality of passageways or sprues provided in the topplate of the mold which intercommunicate each cavity with the spaceabove the top mold plate. In addition, an injection unit is providedwhich comprises an injection piston movable in an open-ended cylindercommonly referred to as a bottomless cylinder. The injection unit isusually affixed to the lower surface of the heated, upper platen of apress and the mold is usually removably placed atop the upper surface ofthe heated, lower platen or ram cap of the press, directly in line withthe injection unit.

In the operation of this apparatus, a quantity of molding compound inexcess of that which would be sufficient to fill all the cavities isplaced on the top plate of the mold, and the press is closed. Duringclosure, the top plate of the mold contacts the lower end of thebottomless cylinder, closing the lower end thereof. As closure of thepress continues, the mold and cylinder move upward relative to theinjection piston, causing the molding compound atop the mold to becomecompressed between the injection piston and the top mold plate and toflow through the various sprues into the respective mold cavities. Theexcess compound in the injection cylinder is maintained undercompression both during filling of the cavities and during the time thatit takes for the heated upper and lower platens to cure the compound inthe filled cavities. This maintains hydraulic pressure on. the top plateof the flashless mold in order to keep the cavities closed during thefilling and curing period (limiting flash formation at the mold partinglines) and in order to prevent backrinding or backflow of the compoundfrom the cavities through the sprues (with the creation of attendant,undesirable blemishes on, and/or changes in, the dimensions of the partsbeing molded in the cavities). In this process, however, the excesscompound in the injection cylinder is cured along with the compound inthe mold cavities and represents waste which is generally scrapped.

Various attempts have been made to improve on the above prior artprocedure in order to overcome the losses inherent in the scrapping ofthe molding compound which is cured in the injection cylinder. One

such attempt culminated in the invention of Herbert F.

Jurgeleit disclosed in U.S. Pat. No. 3,070,843, dated Jan. 1, 1963. Inthat process, a piston-cylinder injection unit is closed by a flexible,metallic plate, which plate not only allows the hydraulic pressure ofthe molding compound to be transmitted to the top mold plate of a mold(single or multiple cavity, flashless or nonflashless) during theinjection cycle (to thereby assist in keeping the mold cavities closedduring such injection), but retains the molding compound in theinjection unit when the molds are thereafter moved away from theinjection unit into a separate heated, curing area. With thisarrangement, curing of the excess com pound in the injection unit may beavoided. However, this is at the expense of providing a plurality ofmolds and a separate curing area. Moreover, when the injection cylinderand mold are separated to facilitate movement of the mold to theseparate curing area, the pressure in the cavities and on the top moldplate is released, allowing, to some degree, backrinding of compoundthrough the sprues and possible flash formation at the parting lines ofthe mold.

Another attempt to overcome the losses inherent in the scrapping ofmolding compound which is cured in the injection cylinder is exemplifiedby the invention of Herbert F. Jurgeleit disclosed in U.S. Pat. No.3,121,918, dated Feb. 25, 1964. In this process, a piston-cylinderinjection unit, which cooperates with a multicavity, clashless mold, isalso closed by a flexible, metallic plate but, instead of moving themold to a separate, heated, curing area to prevent curing of the excesscompound in the injection cylinder, the injection cylinder itself ismoved to a cool area while the mold remains in the heated area and thecompound in the cavities is cured. In this instance, again, theinjection pressure is relieved after the cavities have been filled inorder to allow removal of the injection cylinder. Accordingly,backrinding may occur at such time, resulting in the formation ofblemished parts, parts whose dimensions may fail to match precisely thedimensions of the cavities in which they are formed, and/or parts whosedensity may be less than that required by the specifications for theparts.

SUMMARY OF THE INVENTION Accordingly, it is a principal object of thepresent invention to obviate the formation of waste or scrap within theinjection cylinder of a molding apparatus by insulating theinjectioncylinder from the mold to prevent curing of an excess portionof elastomeric stock remaining within the injection cylinder while thelatter remains in biasing relation with the mold.

It is a further object of the present invention to provide an insulationplate at the end of a bottomless cylinder," the open end of thebottomless cylinder having a cross-sectional area which, in terms of thepressure developed therein, provides a mold closing force that issubstantially greater than the corresponding mold opening forceresulting from the projected area of, and pressure developed in, thecombined mold cavities of the mold. This relationship prevents the moldcavity portions from separating from one another along their mutualparting lines and substantially obviates the seepage of flash formingelastomeric stockat the parting lines of the mold.

It is still a further object of the present invention to provide aninsulation plate between an injection cylinder and a multi-cavity mold,whether the mold be of a flashless or non-flashless construction.

It is another object of the present invention to provide an insulationplate which is to be interpositioned between an injection cylinderand'mold, irrespective of whether the injection cylinder and mold aremovable horizontally or vertically relative to one another.

It is a further object of the present invention to provide an insulationplate which is mounted upon on injection cylinder and interposed betweenthe latter and a mold, the insulation plate being either of fixed naturerelative to the injection cylinder or slightly axially movable relativethereto.

It is another primary object of the present invention to provide amethod of fabricating an insulation plate which, at least in the laststages of the forming of the insulation plate, utilizes the structure ofthe injection cylinder and mold to provide aperture locating referencemarks on the insulation plate.

Briefly stated, the apparatus of the present invention generallycomprises a heated mold having a plurality of mold cavities, anelastomeric stock injection cylinder having an open ended chamber inwhich elastomeric stock is disposable and form which elastomeric stockis transferable, and a heat-resistant, flexible, end insulation plateinterposed between the mold and injection cylinder and having aplurality of apertures which are aligned with corresponding moldcavities to permit transferring of elastomeric stock from the injectioncylinder into the mold cavities. An assembly is provided for moving themold and injection cylinder relative to one another so that an exposedend face presented by the mold cavities is brought into flush pressingengagement with the insulation plate. The injection cylinder includes apiston for exerting pressure in the chamber against the'elastomericstock to expel and transfer at least a portion of the latter therefrominto the mold cavities through the intermediary of the correspondinginsulation plate apertures. The heat-resistant, flexible end insulationplate acts to prevent the heated mold from curing an excess portion ofthe elastomeric stock remaining in the injection cylinder during curingof that portion of the stock which was transferred into the moldcavities.

BRIEF DESCRIPTION OF THE DRAWINGS The above and additional objects andadvantages of this invention will be more clearly understood from thefollowing detailed description thereof when read in conjunction with theaccompanying drawings in which:

FIG. 1 is a fragmentary, schematic, vertical crosssectional view of abottomless injection cylinder having an insulation plate fixed andconstrained against axial movement relative thereto, and an associatedmulticavity, non-flashless mold;

FIG. 2 is a view similar to that of FIG. 1 illustrating the lower endportion of the bottomless cylinder (absent the piston) and insulationplate pressing against the mold in which the mold cavity-definingportions are of the flashless or locally deformable variety;

FIG. 3 is a fragmentary elevational view, partly in section, of a pressillustrating the relationship of the insulation plate with a mold havinginserts for defining the mold cavities, the inserts comprising insertelements which are of the flashless or locally deflectable variety;

'FIG. 4 is an enlarged, fragmentary, partially crosssectional view ofthe lower right-side portion of the press of FIG. 3 incorporating aperforated or apertured baffle plate for use in concomitantly removingscrap from each sprue;

FIG. 5 is a fragmentary, cross-sectional view of the structureillustrated'in FIG. 4, wherein the cylinder and mold are out of biasingrelation with one another after the elastomeric stock has cured and isin a condition for removal from each mold cavity;

FIG. 6 is a fragmentary, cross-sectional view of the relationship of thebaffle plate with scrap removed from the sprue portion of a mold cavity,the baffle plate being in an elevated condition relative to the mold;

FIG. 7 is a schematic, front elevational view of a horizontally movablepress having toggle-linkage actuating members; FIG. 8 is an enlarged,fragmentary, vertical crosssectional view of the press members of FIG. 7biasing against one another through the intermediary of an axiallymovable insulation plate, the mold cavity-defining portions being of theflashless variety; and

FIG. 9 is still a further enlarged fragmentary, vertical,cross-sectional view illustrating more clearly the manner that theaxially movable insulation plate is operatively mounted upon thebottomless injection cylinder.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, andmore particularly to FIG. 1 thereof, the present invention relates totransfer molding apparatus denoted generally by the reference character10. The apparatus 10 includes an axially movable injection cylinder 12(of the bottomless cylinder variety) having an open ended chamber 14 anda lower, inwardly disposed annular flange l6. Beneath the injectioncylinder 12 there is provided an axially movable mold assembly 18(heated conventionally by means not shown) having a base plate 20 inwhich is provided a cylindrical chamber 22, a central plate 24 in whichis provided a cylindrical chamber 26, and an upper plate 28 in which isprovided a cylindrical chamber 30. The plates 20, 24 and 28 aresuperposed upon one another such that their respective chambers 22, 26and 30 are coaxially aligned in communicating relation with one another.

Confined within the cylindrical chamber 22 of the base plate 20 is alower mold portion 32 having an upper face 34 which extends above theupper face 36 of the base plate 20. Arranged within the cylindricalchamber 26 of the central plate 24 is a central mold portion 38 having alower face 40, which rests upon the upper face 34 of the lower moldportion 32, and an upper face 42 which extends above the upper face 44of the central plate 24. Arranged within the cylindrical chamber 30 ofthe upper plate 28 is an upper mold portion 46 having a lower face 48which rests upon the upper face 42 of the central mold portion 38. Theupper mold portion 46 likewise has an upper face 50 and is provided witha plurality of apertures 52 which define respective passagewayscommunicating with a plurality of mold cavities 54 defined by thecooperating mold portions 32, 38 and 46, the central mold portion 38acting to axially space the lower mold portion 32 from the upper moldportion 46 to define the respective cavities 54 therebetween.

Interposed between the mold assembly 18 and the injection cylinder 12,and fixedly mounted upon the latter, is a heat-resistant, flexible, endinsulation plate 56 (the nature of which will be fully discussed below),which is constrained against axial movement relative to the injectioncylinder 12 by means of screws 58 or the like. A plurality of apertures60 are provided in the insulation plate 56, the apertures 60 beingrespectively aligned with the passageways 52 provided in the upper moldportion 46. Each of the apertures 60 in the insulation plate 56 acts tosupport and confine respective low-friction annular inset elements 62which likewise communicate with the respective mold cavities in the moldassembly 18, each of the inset elements 62 being constituted of amaterial similar to that available under the trademark Teflon, e.g.polytrifluorochloroethylene, polytetrafluoroethylene, etc.

In operation, elastomeric stock 64, in the nature of natural orsynthetic rubber, alkyl-phenol-resin, thermosetting resins such asphenol-, urea-, or melamineformaldehyde-resin, epoxy resin,heat-resistant silicones, and acrylic resins, etc., is deposited intothe injection cylinder 12, between the insulation plate 56 and astationary piston 66. The piston 66 is disposed within the injectioncylinder 12 and defines therewith the chamber 14.

The mold assembly 18 is then elevated into engagement with the injectioncylinder 12 such that the heatresistant, flexible, end insulation plate56 lies flush and presses against the upper end face 50 of the uppermold portion 46 of the mold assembly 18. The low-friction annular insetelements 62 are now in direct axially communicating relation with thepassageways 52 in the upper mold portion 46 which communicate with therespective mold cavities 54. As the mold assembly 18 is moved furtherupwardly, it carries therewith the injection cylinder 12 and reduces theaxial extent of the chamber 14 (this because the piston 66 remainsconstrained against axial movement relative to the upwardly movinginjection cylinder 12).

Thus, as the upwardly moving injection cylinder 12 causes a reduction inthe axial extent of the chamber 14, a portion of the elastomeric stock64 is expelled and transferred into the respective mold cavities 54.

During the subsequent curing of the injected molding material, theheat-resistant nature of the insulation plate 56 prevents curing of theexcess elastomeric stock 64 remaining in the chamber 14 despite theremaining biasing relationship of the mold assembly 18 with theinjection cylinder 12.

The low friction annular inset elements 62 act to prevent theelastomeric stock 64 from adhering to the periphery of the apertures 60of the insulation plate 56 as the elastomeric stock passes therethrough.Because of the flexible nature of the insulation plate 56, the latter isable to lie substantially uniformly flush against the entire end face 50of the upper mold portion 46 to thereby obviate seepage of elastomericstock 64 at the parting line therebetween.

As is evident from FIG. 1, the projected area of the chamber 14 isgreater than the combined projected area of all of the cavities 54, thisensuring that the clamping pressure, that pressure which maintains themold assembly 18 in operative biasing association with the injectioncylinder 12 and which is substantially identical to the injectionpressure, namely the pressure necessary for causing a transfer of theelastomer stock from the chamber 14 into each mold cavity 54, issufficient to prevent the mold portions 32, 38 and 46 from separatingfrom one another along their respective parting lines, separation whichmay otherwise result in an over-filling of the cavities 54, seepage atthe mold parting lines and the formation of flash upon the moldedproduct.

Pursuant to the principal concept of the present invention, theinsulation plate 56 should be of rather thin flexible nature to minimizethe axial extent of the passageway that the elastomeric stock 64 musttraverse as it is transferred from the chamber 14 into the respectivemold cavities 54. However, the insulation plate 56 should be ofsufficient thickness to prevent the portion of the elastomeric stock 64remaining in the chamber 14 from being cured during the curing of thatportion transferred into the mold cavities 54.

In this respect, the particular nature or composition of the elastomericstock 64 that is to be transferred from the chamber 14 into the moldcavities 54, in conjunction with the particular temperatures that aredeveloped, such as in the range of IOO200C., will de termine thenecessary thickness of the insulation plate 56. Moreover, it has beendetermined that the insulation plate 56 should be preferably constitutedof a mixture of asbestos fibers and a thermosetting resin, such asphenol resin or the like, and appropriately cured such that it isimparted with the necessary flexibility and heat-resistant qualities. Itis preferable that the thermal conductivity of the insulation plate 56be less than about 0.5 kcal/m/hr/K, but it may exceed about 0.05kcal/m/hr/K. The compression resistance of the insulation plate 56 attemperatures of approximately l-200C. should be not less than from aboutZOO-2,000 kglcm The compression resistance rates the capacity of theplate 56 to withstand a compression load without undergoing permanentdeformation. The modulus of elasticity of the insulation plate 56 shouldbe at least, and preferably greater than, about 1.5Xl0 kg/cmAccordingly, when the insulation plate 56 is provided with such orsimilar properties, it will most effectively resist heat transfer fromthe heated mold cavities 54 to the remainder of the elastomeric stockconfined within the chamber 14 of the injection cylinder 12. This willpermit the mold assembly 18 to be maintained in effective pressingrelation with the injection cylinder 12 while the transferredelastomeric stock within the confines of the mold cavities 54 is cured,and to obviate waste which would normally result upon curing of theremainder of the elastomeric stock 64 in the chamber 14.

Alternatively, the flexible nature of the insulation plate 56 can beutilized with flashless or locally deformable mold portions in a mannerillustrated generally in FIG. 2. In this respect, the mold portions 32,38 and 46 illustrated in FIG. I are generally of inflexible nature andwill not yield relative to one another when pressure is exertedthereagainst by the flexible insulation plate 56. However, asillustrated in FIG. 2, the rigid upper mold portion 46 of FIG. 1 may bereplaced with a flexible upper mold portion 46' having thin, flexiblemembranes 68 between respective segments thereof separated by voids 70.The flexible membranes 68 divide the mold portion 46', through theintermediary of the respective voids 70 above each of the membranes 68,into the respective segments which may be flexed relative to one anotherand likewise relative to the central mold portion 38 therebelow. Thisobviates parting line spacing due to tolerance inadequacies not overcomeduring the manufacture of the mold portions. Such a mold portion 46'prevents the formation of flash along the parting line separating thecentral mold portion 38 from the upper mold portion 46', immediatelybelow each of the membranes 68.

Referring now to FIGS. 3-6, the press 100 there shown utilizes aninsulation plate of the nature described above. The press 100, which isof the type used for transfer or compression molding, is provided with abase 102 and upright guide rods 104 which support a stationarycross-head 106 by means of fastening nuts 108. The stationary cross-head106 supports therebeneath a stationary upper heating platen 110 providedwith a plurality of heating channels 112 in which steam or some otherconventional heating medium is confined. A downwardly facing stationarypiston 114 is centrally secured to the underside of the upper heatingplaten 110 and cooperates with a bottomless cylinder plate 116 having anupper open end 118, and a lower open end 120. Suitably affixed to thebottom face of the cylinder plate 116, as by means of screws 121 or thelike, is an insulation plate 122 which overlies the lower open end 120of the cylinder plate. The upper open end 118 of the latter, and thusthe cylinder bore, is closely matched in size and configuration, to thepiston 114.

The bottomless cylinder plate 116 is suspended upon, and is axiallymovable relative to, the stationary crosshead 106 by means of aplurality of elongate, bolt-like guide rods 124 threadedly affixed tothe plate. The rods 124 extend slidably through respective bores orpassageways 126 formed in the platen 110, each passageway 126 having anupper wider portion 126a to slidably receive a wide head 124A of eachrod 124, and a lower narrower portion 1268 to closely slidably receivethe shank of the associated bolt and simultaneously to prevent the headl24A thereof from passing downwardly therethrough. Each lower narrow.bore portion 126B thus defines the lowermost limit of downward movementof the cylinder plate 116. The rods'l24 extend upwardly through bores128 in the cross-head 106. these bores being wide enough to freelyaccommodate the bolt heads 124A.

A plurality of downwardly open recesses 130 (only one is shown) isprovided in the stationary upper heating platen 110, each recessreceiving and seating a respective compression spring 132 arranged inaxially surrounding relation to a guide stud 134 projecting up wardlyinto the recess and affixed to the upper portion of the bottomlesscylinder plate 116. The compression springs 132 act to urge thebottomless cylinder plate 1 16 toward its at-rest or lowermost suspendedposition.

Centrally arranged in the base 102 is a bore 136 in which is disposed avertically movable ram 138 supporting at its upper end a lower movableheating platen 140 having heating channels 142 therein in which isprovided a suitable heating medium such as steam or the like. Mountedupon the upper surface of the lower movable heating platen 140 is athree-plate mold structure which comprises a base plate 144, a centralplate 146 and an upper plate 148. The base plate 144 (see FIG. 4) isprovided with an array of recesses 150, the central plate 146 with anarray of recesses 152 aligned with the underlying recesses 150,respectively, and the upper plate 148 with an array ofrecesses 154aligned with the underlying recesses 152. Disposed in the variousrecesses are respective mold cavity-defining inserts, each group of suchinserts comprising animperforate lower mold insert 156, an annularcentral cavitydefining insert 157, and an upper sprue'insert 158. Thesprue openings in the upper inserts 158 communicate with respectiveapertures 160 formed in the insulation plate 122. Mounted in each of theapertures 160 in the insulation plate 122 is a respective low-frictionannular inset 162 of Teflon or the like.

As best illustrated in FIGS. 4 and 5, the lower surface of theinsulation plate 122 is provided with a coating or liner 164, the natureof which will be further clarified below, and a baffle plate 166 isremovably mounted on the upper mold plate 148 between the latter and theliner 164. The baffle plate 166 is provided with a plurality ofapertures 168 which are of reduced diameter and are aligned respectivelywith the sprue openings defined by the mold inserts 158 located in theupper mold plate 148.

In operation, elastomeric stock 170, in biscuit form, is initiallydisposed in the space between the lower surface of the piston 114 andthe upper surface of the insu lation plate 122. The ram 138 is thenelevated, causing the lower, movable heating platen 140 to ascend untilthe baffle plate 166 engages the liner 164 or the insulation plate 122.The heating medium in the heating channels 112 acts at this stage to aidin the conversion of the elastomeric stock 170 from the form of agenerally solid biscuit to a more fluid mass, but the heat isinsufficient for curing the elastomeric stock 170. This permits aportion of the elastomeric stock 170 to be forced through thepassageways in the low-friction annular insets 162 of the insulationplate 112.

As the lower heating platen 140'then continues to rise, the bottomlesscylinder plate 116 is likewise caused to ascend relative to the piston114 until the latter enters into the chamber 118 of thebottomlesscylinder plate 116, causing the elastomeric stock 170 todisperse uniformly over the entire upper surface of the insulation plate122 to be expelled in part through the low-friction annular insets 162in the latter.

The initial quantity of the elastomeric stock 170 is in excess of thatrequired for filling the mold cavities defined by the cooperating lower,central and upper mold inserts 156, 157 and 158, respectively. Thus,there is a substantial amount of elastomeric stock 170 which remainswithin the confines of the chamber defined in the bottomless cylinderplate 116 at the end of the injection stage. This ensures that the fluidinjection pressure required for expelling and transferring a portion ofthe elastomeric stock 170 into the various mold cavities can also bemaintained after and even though the cavities are all filled withmolding compound.

The heat provided by the heating medium within the heating channels 142of the lower movable platen 140 is sufficient for curing the portion ofthe elastomeric stock 170 transferred into the mold cavities, the curingtaking place while the bottomless cylinder plate 116 and platen 140 arein contact with one another through the intermediary of the insulationplate 122. The insulation plate 122, however, serves to prevent curingof the elastomeric stock remaining within the confines of the bottomlesscylinder plate 116. At the same time, the flexible nature of insulationplate 122 ensures that the fluid pressure in the cylinder can beutilized for locally deflecting the mold inserts 156, 157 and 158, whichare of the flashless or locally deflectable variety, relative to oneanother, so that the latter may deflect where necessary to seal any gapsbetween their respective parting lines and obviate the formation offlash which may otherwise form at the parting lines.

Thereafter, at the end, or at least during the final stages of the curecycle of the elastomeric stock 170 transferred into the mold cavities,the lower heating platen 140 is retracted and caused to descent relativeto the upper stationery platen 110, which causes the springs 132 to movethe bottomless cylinder plate 116 into its lowermost, at-rest, suspendedposition. When the lower heating platen 140 is sufficiently lowered, oris retracted sufficiently remote from the lower-most suspended positionof the bottomless cylinder plate 116, as illustrated in FIG. 5, thatinaccessible minute portion of the elastomeric stock 170 confined ineach of the low-friction annular insets 162, respectively, tearsmedially into two portions, one of which remains in adherance with thatportion of the elastomeric stock 170 remaining in the chamber of thebottomless cylinder plate 116, and the other of which remains inadherence with the portion of elastomeric stock 170 transferred into themold cavities.

In this respect, because of the reduced diameter of the apertures 168 inthe baffle plate 166, the latter acts to prevent the cured portion ofthe elastomeric stock 170 within the mold cavities from being pulled outof the confines of these cavities when the lower movable heating platen140 is retracted from the insulation plate 122. Instead, the elastomericstock portions within the confines of the low-friction annular insets161 rupture, for example along the line 172 illustrated in FIGS. and 6.Upon retraction of the platen 140, the thickness of the insulation plate122 is, of course, such as to prevent the portions of the elastomericstock remaining within the annular insets 162 from curing, so that thoseportions may be thereafter injected into the mold cavities during thenext transfer cycle.

As illustrated in FIG. 6, the baffle plate 166 may thereafter be liftedoff the upper plate 148, thereby tearing minute conical portions 174 ofthe cured elastomeric stock out of the upper sprue inserts 158 and fromthe remaining molded products formed within the cavities. Since theconical extent of each sprue is minimal, the baffle plate, upon beinglifted, will concurrently tear off each of the conical portions 174 asscrap.

Pursuant to a principal concept of the present invention, the insulationplate 122 and the liner 164 provided along the lower face thereof, areboth of heat resistant, flexible, insulatory nature and may be formedinto a composite unit by utilizing the apparatus of FIG. 3 in a simpleand effective manner. In this respect, both the insulation plate 122 andthe liner 164 are constituted preferably of asbestos fibers impregnatedwith a preferably thermosetting resin, e.g., phenol resin or the like,the thickness of the liner being at most approximately one-tenth thethickness of the insulation plate 122, the latter being preferably aboutmilimeters in thickness.

Generally speaking, the insulation plate 122 is initially curedentirely, whereas the liner 164 is left either uncured or only partiallycured after being shaped into a conforming disc-like configuration. Theliner 164 is then superposed onto the lower face of the insulation plate122, preferably after the latter is fixedly mounted upon the lowersurface of the bottomless cylinder plate 116, e.g., by means of screws121. Thereafter, the heated, lower movable platen is moved upwardly topress the upper mold plate 148 against the liner. The sprues in theupper sprue inserts 158 thereby form impressions in the exposedunderside of the liner 164, this because the latter is initially in aless than fully cured condition and will readily receive impressionswhen biased against a stenciling medium such as the sprue inserts 158.Moreover, confronting profile irregularities in the plate 148 formcomplimentary profile irregularities in the exposed underside of theliner 164 which are useful, when cycling the apparatus, for intermeshingwith one another to seal the parting line between the liner 164 and theplate 148. As the impressions are formed, the liner 164 undergoesadditional curing and hardening. Preferably, though not necessarily, thebottomless cylinder plate 116 is partially filled with elastomeric stockduring the period in which the upper mold plate 148 presses against theliner 164 to form the impressions in the latter. The small portion ofelastomeric stock acts to hydraulically equalize the pressure againstthe insulation plate 122 by the piston 114 so as to compensate forvarious profile irregularities which may exist in the face of the piston114 which confronts the insulation plate 122.

Thereafter, the lower heating platen 140 is retracted from both theliner 164 and insulation plate 122 thereby permitting, by suitablemeans, boring through both the insulation plate and the liner at theimpressions formed in the latter, to form the apertures in the compositearray of the liner 164 and insulation plate 122 required forestablishing communication between the cylinder chamber and the sprues.The said apertures are also countersunk to receive, subsequently, thelow-friction annular insets 162.

It has further been determined to be advantageous to interposition alow-friction material, such as silver-like such as aluminum foil,between the lower exposed face of the liner 164 and the upper exposedsurface of the mold plate 148 prior to the latter being pressed againstthe liner 164. This thin layer of metallic or silver-like foil, uponbeing subjected to the liner-curing pressure, will adhere to the liner164 and prevents the upper plate 148 from adhering to the liner 164 whenthe latter undergoes its final curing. The foil thus will permitretraction of the plate 148 away from the liner 164 upon appropriateretraction of the lower heating platen 140 while still leavingbore-defining impressions in the liner 164. The metallic foil adheringto the liner 164 also acts to provide the latter with a capacity tosubsequently resist adhering to the upper plate 148 upon repeatedcontact with the latter during cycling of elastomeric stock into therespective mold cavities.

Each of the embodiments described above has been characterized asincluding an insulation plate which is fixedly mounted upon thebottomless cylinder or injection unit and operates to thermally isolatethe mold from the elastomeric stock confined within the cylinder.However, the invention likewise contemplates the utilization of aninsulation plate which is mounted upon the injection unit so that it isat least slightly movable axially relative to the injection unit forpurposes to be further clarified below.

In this respect, referring now to FIGS. 7-9 and more particularly toFIG. 7, still a third embodiment of the apparatus pursuant to thepresent invention is there illustrated which likewise relates totransfer molding apparatus denoted by the reference character 200. Theapparatus 200 includes a base 202 upon which is provided an upstandingsupport block 204 carrying a plurality of horizontal guide rods 206, andadjacent which is provided a toggle-linkage support and actuationassembly 208. The assembly 208 is operatively associated with atoggle-linkage array 210 (of conventional nature) for effecting movementof a mold assembly 212 along the horizontal guide rods 206, toward andaway from a stationary injection unit 214 affixed to and supportingopposite ends 215 of the rods 206.

Operatively associated with the injection unit 214 is an elastomericstock input source 216 which communicateswith the injection unit 214through the intermediary of an injection cylinder 218 (of bottomlesscylinder variety) in which is constrained a movable piston 220 .(FIG.8). The piston 220 is associated with a support block and pistonactuation unit 222 for movement relative to the interior of theinjection cylinder 218, as will be clarified belowv The injectioncylinder 218 comprises an adapter 224, the interior of the lattercommunicating axially with the piston-confining chamber 226 within theinjection cylinder 218. A transition chamber 228 is disposed between,and intercommunicates, the adapter 224 and chamber 226.

The adapter 224 is provided with a cylindrical flange or wall 230 whichmerges internally with a generally frustoconical, outwardly divergingwall 232, the latter centrally communicating with the transition chamber228 which diverges from a point at the end of the piston-confiningchamber 226 to the interior of the adapter 224. The diverging wall-232of the adapter 224 is provided with a plurality of channels 233 in whichis disposed an appropriate heating or cooling medium such as steam,water, or oil, etc.

A heat-resistant, flexible, end insulation plate 234 having an enlargedexposed flange 236 is operatively mounted on the adapter 224'andconfronts the mold assembly 212. In this respect, the insulation plate234 may be simply held frictionally along the-periphery thereof by theadapter 224. Alternatively, the exposed flange 236 of the insulationplate 234 may be provided with an array of circumferentially spaced,axially extending, recesses 238 in each of which is slidably received ahead 240 of a respective mounting bolt 242, each of the mounting bolts242 terminating in an opposite end 244 which is threadedly, orotherwise, fixed to the cylindrical flange 230 of the adapter 224. Theconcealed body portion 246 of reduced diameter of the insulation plate234 is slidably received within the confines of the cylindrical flange230 of the adapter 224.

The end insulation plate 234 is provided with an array of apertures 248in which are confined respective low-friction annular insets 250 whichare generally T- shaped in cross-section and communicate with the moldassembly 212. The mold assembly 212 is provided with an end plate 252along which is superposed a heatresistant insulation sheet 254constituted of any suitable insulatory material having an appropriatethickness for preventing the end plate 252 from overheating as a resultof heat generated by a heating platen 256. The platen 256 is providedwith heating channels 258 for heating the mold assembly 212 and issuperposed along the insulation sheet 254 opposite that surface of thelatter which is in contact with the end plate 252.

Superposed along the heating platen 256 is an assembly of mold platescomprising an inner or bottom mold plate 260, a central mold plate 262superposed upon the inner mold plate 260, and an outer mold plate 264superposed upon the central mold plate 262. The mold plates 260, 262 and264 are each provided with an array of apertures, the apertures of eacharray being coaxially aligned with respective apertures of the otherarrays. Each group of aligned apertures acts as a receptacle for arespective one of a plurality of inner mold inserts 266, one of aplurality of central cavity-defining mold inserts 268, and one of aplurality of outer sprue inserts 270, eachresting upon one another fordefining respective mold cavities into which elastomeric stock may beinjected and cured. The inserts 266, 268 and 270, respectively, are as agroup of flashless or locally 'deflectable nature, and function, bymoving slightly relative to one another, in the manner described abovefor the mold inserts illustrated in FIGS. 3-6.

A plurality of circumferentially spaced bolts 272 act to affix the innermold plate 260 to the heating platen 256, whereas the central mold plate262 and outer mold plate 264 are detachably associated (FIG. 9) with oneanother, with the inner mold plate 260 and with an apertured baffleplate 274 (by conventional means not shown). The baffle plate 274 isexposed and confronts the insulation plate 234 to be biased against thelatter, as will be described below.

As best illustrated in FIG. 9, the insulation plate 234 is surrounded bya flexible gasket or sealing ring 276 internally of which extends aflexible annular rib 278 which rests upon the interior of the insulationplate 234, the flexible rib 278 deforming slightly to optimize sealingof the movable insulation plate 234 relative to the adapter 234 duringinjection'of elastomeric stock 280 into the respective mold cavities inthe mold assembly 212.

In operation, the toggle-linkage array 210, which is only schematicallyillustrated but, as generally understood, is comprised of a plurality oflinks which are movable into an over-center locking position, acts tomove the mold assembly 212 toward the injection cylinder 218.Elastomeric stock 280 is introduced into the piston-confining chamber226 of the injection cylinder 218, and is of such a quantity that it isin excess of that which is necessary to fill each and every one of themold cavities. The heating medium within the confines of the heatingchannels 233 acts to impart a degree of fluidity to the elastomericstock 280, so that when the latter is acted upon by the piston 220, itwill readily flow along the frustoconical diverging wall 232 of theadapter 224,'through the respective apertures within the low-frictionannular insets 250, while exerting a uniform pressure against theinsulation plate 234 in an axially outward direction thereby causing theinsulation plate 234 to move to its axially outermost position.

As the insulation plate 234 is caused to move toward its axiallyoutermost position, the insulation plate 234 engages the baffle plate274 mounted upon the mold assembly 212 and exerts a likewise uniformpressure thereagainst. The baffle plate 274 which is likewise somewhatflexible acts to transmit and exert a pressure against each and everyone of the mold inserts 266, 268 and 270 thereby causing the latterinserts to deflect locally relative to one another and close all, if anygaps at the parting lines therebetween. As the gaps at the parting linesbetween the mold inserts are diminished,

there is likewise diminished the likelihood of the formation of flashupon the portion of elastomeric stock transferred into the moldcavities.

As the movement of the piston 220 toward the adapter 224 continues, ofcourse, it causes a prescribed quantity of the elastomeric stock 280 tobe expelled through the low-friction annular insets 250 and injectedinto the confines of the mold cavities. The portion of the elastomericstock 280 tranferred into the mold cavities then undergoes curing bymeans of the heat supplied by the heating medium confined within theheating channels 258 of the heating plate 256. However, because of theinterposition of the insulation plate 234 between the mold cavities andthe interior of the adapter 224, the remainder of the elastomeric stock280 within the confines of the adapter 224 is prevented from curingdespite the continued engagement of the heated mold assembly 212 withthe stationary injection unit 214.

At the end of the curing process, or at least toward the very finalstages of curing, the toggle-linkage array 210 is operated to retractthe mold assembly 212 away from the end insulation plate 234, permittingemptying of the molded products from the mold cavities. Since the baffleplate 274 has been moved away from the insulation plate 234, the lattermay be caused to move into its extreme, axially, outermost position bythe stock 280 remaining in the cylinder 219, this by shifting the pistonslightly toward the adapter 224, to await return of the mold assembly212, after emptying of the latter, into engagement therewith.

In this respect, at the end of the curing process the baffle plate 274can be utilized for concurrently removing elastomeric scrap that hascured within the confines of the sprues of the outer sprue inserts 270,and the mold cavities can then be emptied for recycling into operativeassociation with the injection cylinder 218. Once vacant, the moldcavities can then be moved, through the intermediary of thetoggle-linkage array 210, into proximity with the insulation plate 234.The baffle plate 274 will then engage the insulation plate 234 and movethe latter inwardly of the adapter 224 thereby causing, without anymovement of the piston 220 whatsoever, expulsion and transferring of afurther portion of elastomeric stock 280 into the mold cavities.

Thus, the apparatus pursuant to the embodiment of FIGS. 7-9 permitsfilling of the mold cavities by two different methods. In one, thepiston 220 can be utilized, as discussed above, for causing expulsion ofelastomeric stock 280 from the confines of the adapter 224 into the moldcavities. In the alternative method, the adapter 224 can be filled tosuch an extent that, upon retraction of the mold assembly 212 and aslight forward movement of the piston 220 during retraction of the moldassembly 212, the insulation plate 234 is moved to its extreme, axiallyoutermost position. Upon return movement of the mold assembly 212thereafter into engagement with the insulation plate 234, the latter isforced slightly into the interior of the adapter 224, causing expulsionof a portion of the elastomeric stock 280 into the confines of the moldcavities for curing.

Numerous alterations of the structure herein disclosed will suggestthemselves to those skilled in the art. However, it is to be understoodthat the present disclosure relates to preferred embodiments of theinvention which are for purposes of illustration only and not to beconstrued as a limitation of the invention.

What is claimed is:

1. Apparatus for molding elastomeric stock, said apparatus comprising: amold provided with a plurality of mold cavities for shaping and curingelastomeric stock in the form of said cavities; an elastomeric stockinjection unit having a chamber in which elastomeric stock is disposableand can be subjected to pressure for transfer from said chamber; aheat-resistant, flexible insulation plate positioned intermediate saidmold and said injection unit, said insulation plate having flat,opposed, side faces which are capable of flexing in response to pressurethereagainst, at least one of said side faces forming a parting linebetween said mold and said injection unit, said insulation plateincluding a plurality of apertures therethrough for intercommunicatingsaid injection unit with said mold cavities; means for heating saidmold; and means for moving said mold and said injection unit relative toone another and said insulation plate in such a manner that said mold onone side face of said insulation plate and said injection unit and saidelastomeric stock in said injection unit on the other side face of saidinsulation plate are pressed against the opposite side faces of saidinsulation plate to flexibly conform said insulation plate to, andtightly seal, vary ing surface irregularities of said mold and saidinjection unit pressing thereagainst; whereby upon exertion of pressurein said chamber against said elastomeric stock a portion of said stockwill be expelled from said chamber and concurrently transferred througheach of said plurality of apertures into the cavities of said heatedmold to fill said cavities under substantially uniform fluid pressurewithout seepage of said elastomeric stock between said mold or saidinjection unit and said insu lation plate, said insulation plate servingto thermally insulate the remaining portion of elastomeric stock in saidchamber from said heated mold, without separation of said mold or saidinjection unit from said insulation plate or relaxation of said fluidpressure, in order to prevent the curing of said remaining portion ofstock with the curing of said transferred portion of stock.

2. Apparatus as claimed in claim 1, wherein said mold includes anexposed end face and wherein said insulation plate is affixed to saidinjection unit and serves to enclose one end of said chamber, said endface of said mold and one side face of said insulation plate being inconfronting, separable relationship with one another.

3. Apparatus as claimed in claim 2, wherein at least an endmost axialportion of said chamber directly confronts and is laterally coextensivewith said insulation plate, said insulation plate having a projectedarea, pressurized by said elastomeric stock, greater than the combinedprojected area of said mold cavities.

4. Apparatus as claimed in claim 2, wherein said mold includes aplurality of mating sections detachably superposed upon one anotherwhich cooperatively define said mold cavities.

S. Apparatus as claimed in claim 4, wherein said mating sections of saidmold are substantially inflexible.

6. Apparatus as claimed in claim 4, wherein said mating sections of saidmold are at least partially flexible and deform locally at each of saidcavities in response to pressure exerted thereagainst via saidinsulation plate.

7. Apparatus as claimed in claim 2, wherein said mold includes meansdefining a plurality of insertreceiving recesses, and a plurality ofmovable groups of inserts removably disposed in said recesses,respecmeans defining said plurality of insert-receiving recessesincludes a plurality of plates superposed upon one another, with therecesses in each plate being aligned with the corresponding recesses ofthe other plates, each of said recesses receiving a respective one ofthe inserts of the respective insert group.

9. Apparatus as claimed in claim 2, wherein said mold and said injectionunit are movable vertically relative to one another.

10. Apparatus as claimed in claim 2, wherein said mold and saidinjection unit are movable horizontally relative to one another.

11. Apparatus as claimed in claim 2, wherein said insulation plate isfixedly connected to said injection unit.

12. Apparatus as claimed in claim 11, wherein said injection unitincludes a stationary piston and a cylinder axially movable relativethereto, said mold being supported for axial movement relative to saidpiston, such that said mold is movable into engagement with saidcylinder and is then effective to move the the latter relative to saidpiston to reduce the axial extent of said chamber, thereby to cause aportion of said elastomeric stock to be injected from said chamber intosaid mold cavities.

13. Apparatus as claimed in claim 2, including a multi-apertured baffleplate detachably interpositioned between said insulation plate and saidexposed end face of said mold, said apertures in said baffle plate beingaligned with corresponding ones of said apertures in said insulationplate, said apertures of said baffle plate beingof reduced diameter andconstituting means for permitting break-away separation of the moldedproducts formed in said mold cavities from elastomeric stock scrapform'edin part in the s prue portions of said mold adjacent saidinsulation plate.

14. Apparatus as claimed inclaim 2, wherein said insulation plate has athermal-conductive capacity which is substantially less than thethermal-conductive capacity of iron.

15. Apparatus as claimed in claim 14, wherein the thermal conductivityof said insulation plate is in the range of ODS-0.5 kcal/m/hr./K.

16. Apparatus as claimed in claim 2, wherein said insulation plate has acompression resistance in the range of ZOO-2,000 kg./cm. at temperaturesbetween l80200C.

17. Apparatus as claimed in claim 2, wherein said insulation plate has amodulus of elasticity of at least 1.5 X 10 kg./cm.

18. Apparatus as claimed in claim 2, wherein said insulation plate isconstituted of an asbestos fiber and thermoset resin mixture.

19. Apparatus as claimed in claim 18, wherein said thermoset resincomprises phenol resin.

20. Apparatus as claimed in claim 2, wherein said insulation plateincludes, on the side face thereof which confronts and contacts saidmold, aa thin layer of hardenable, flexible material which undergoesincreasing hardening when subjected to the heat and pressure of saidheated mold, said layer having on the surface thereof facing said mold aprofile complementary to the profile of the surface of said mold incontact therewith. V

' 21. Apparatus as claimed in claim 20, wherein said thin layer isconstituted of an asbestos fiber and thermoset resin mixture.

22. Apparatus as claimed in claim 21, wherein said thermoset resin ofsaid thin layer comprises phenol resin.

23. Apparatus as claimed in claim 2, wherein said insulation plate has athickness sufficient to maintain a temperature gradient thereacross suchthat, when the side face thereof which confronts said mold is at thecuring temperature for said elastomeric stock in said mold cavities, thetemperature on the opposite side face of said insulation plate whichconfronts said chamber remains at a temperature insufficient to causethe excess elastomeric stock remaining in said chamber to become cured.

24. Apparatus as claimed in claim 2, including respective annular insetsdisposed in said apertures of said insulation plate, said annular insetsbeing constituted of a material having an adhesion resistance to saidelastomeric stock greater than that of said insulation plate.

25. Apparatus as claimed in claim 24, wherein said annular insets areconstituted at least in part of polytetrafluoroethylene or a likematerial.

26. Apparatus for molding elastomeric stock, said apparatus comprising:a heated mold provided with a plurality of mold cavities for shaping andcuring elastomeric stock in the form of said cavities; an elastomericstock injection unit having a chamber in which elastomeric stock isdisposable and can be subjected to pressure for transferfrom saidchamber; a multi-apertured, heat-resistant, flexible insulation platecarried by said injection unit at an end of said chamber, the aperturesof said plate communicating with corresponding ones of said I moldcavities; a correspondingly multiapertured, flexible liner superposedalong and affixed to one side face of said plate and confronting saidmold,

said liner having pre-formed profile irregularities, along the surfacethereof which confronts and forms a parting line with said mold, whichare complimentary to and under pressure flexibly intermesh with profileirregularities of the confronting surface of said mold; and means formoving said mold and injection unit relative to one another such thatsaid confronting surface of said mold is pressed against said liner andsaid complimentary profile irregularities of each sealingly intermeshwith one another; whereby, without separation of said mold and injectionunit, upon exertion of pressure in said chamber against said stock aportion of the latter will be expelled from said chamber and transferredthrough the apertures in said plate and liner into said mold cavitieswithout seepage of elastomeric stock at the parting line between saidmold and liner and without curing of elastomeric stock in said injectionunit curing curing of elastomeric stock in said mold cavities.

27. Apparatus as claimed in claim 26, including means for heating saidmold, said plate being made of thermal insulatory material.

28. Apparatus as claimed inclaim 27, wherein said liner and said plateare each constituted of an asbestos fiber and thermoset resin mixture.

1. Apparatus for molding elastomeric stock, said apparatus comprising: amold provided with a plurality of mold cavities for shaping and curingelastomeric stock in the form of said cavities; an elastomeric stockinjection unit having a chamber in which elastomeric stock is disposableand can be subjected to pressure for transfer from said chamber; aheat-resistant, flexible insulation plate positioned intermediate saidmold and said injection unit, said insulation plate having flat,opposed, side faces which are capable of flexing in response to pressuretherEagainst, at least one of said side faces forming a parting linebetween said mold and said injection unit, said insulation plateincluding a plurality of apertures therethrough for intercommunicatingsaid injection unit with said mold cavities; means for heating saidmold; and means for moving said mold and said injection unit relative toone another and said insulation plate in such a manner that said mold onone side face of said insulation plate and said injection unit and saidelastomeric stock in said injection unit on the other side face of saidinsulation plate are pressed against the opposite side faces of saidinsulation plate to flexibly conform said insulation plate to, andtightly seal, varying surface irregularities of said mold and saidinjection unit pressing thereagainst; whereby upon exertion of pressurein said chamber against said elastomeric stock a portion of said stockwill be expelled from said chamber and concurrently transferred througheach of said plurality of apertures into the cavities of said heatedmold to fill said cavities under substantially uniform fluid pressurewithout seepage of said elastomeric stock between said mold or saidinjection unit and said insulation plate, said insulation plate servingto thermally insulate the remaining portion of elastomeric stock in saidchamber from said heated mold, without separation of said mold or saidinjection unit from said insulation plate or relaxation of said fluidpressure, in order to prevent the curing of said remaining portion ofstock with the curing of said transferred portion of stock.
 2. Apparatusas claimed in claim 1, wherein said mold includes an exposed end faceand wherein said insulation plate is affixed to said injection unit andserves to enclose one end of said chamber, said end face of said moldand one side face of said insulation plate being in confronting,separable relationship with one another.
 3. Apparatus as claimed inclaim 2, wherein at least an endmost axial portion of said chamberdirectly confronts and is laterally coextensive with said insulationplate, said insulation plate having a projected area, pressurized bysaid elastomeric stock, greater than the combined projected area of saidmold cavities.
 4. Apparatus as claimed in claim 2, wherein said moldincludes a plurality of mating sections detachably superposed upon oneanother which cooperatively define said mold cavities.
 5. Apparatus asclaimed in claim 4, wherein said mating sections of said mold aresubstantially inflexible.
 6. Apparatus as claimed in claim 4, whereinsaid mating sections of said mold are at least partially flexible anddeform locally at each of said cavities in response to pressure exertedthereagainst via said insulation plate.
 7. Apparatus as claimed in claim2, wherein said mold includes means defining a plurality ofinsert-receiving recesses, and a plurality of movable groups of insertsremovably disposed in said recesses, respectively, each of said insertgroups including a plurality of mating elements cooperatively defining arespective mold cavity, corresponding portions of said insert groupspresenting said exposed end face of said mold and being locally movablein response to pressure exerted thereon via said insulation plate. 8.Apparatus as claimed in claim 7, wherein said means defining saidplurality of insert-receiving recesses includes a plurality of platessuperposed upon one another, with the recesses in each plate beingaligned with the corresponding recesses of the other plates, each ofsaid recesses receiving a respective one of the inserts of therespective insert group.
 9. Apparatus as claimed in claim 2, whereinsaid mold and said injection unit are movable vertically relative to oneanother.
 10. Apparatus as claimed in claim 2, wherein said mold and saidinjection unit are movable horizontally relative to one another. 11.Apparatus as claimed in claim 2, wherein said insulation plate isfixedly connected to said injection unit.
 12. Apparatus as claimed inclaim 11, wherein said injection unit includes a stationary piston and acylinder axially movable relative thereto, said mold being supported foraxial movement relative to said piston, such that said mold is movableinto engagement with said cylinder and is then effective to move the thelatter relative to said piston to reduce the axial extent of saidchamber, thereby to cause a portion of said elastomeric stock to beinjected from said chamber into said mold cavities.
 13. Apparatus asclaimed in claim 2, including a multi-apertured baffle plate detachablyinterpositioned between said insulation plate and said exposed end faceof said mold, said apertures in said baffle plate being aligned withcorresponding ones of said apertures in said insulation plate, saidapertures of said baffle plate being of reduced diameter andconstituting means for permitting break-away separation of the moldedproducts formed in said mold cavities from elastomeric stock scrapformed in part in the sprue portions of said mold adjacent saidinsulation plate.
 14. Apparatus as claimed in claim 2, wherein saidinsulation plate has a thermal-conductive capacity which issubstantially less than the thermal-conductive capacity of iron. 15.Apparatus as claimed in claim 14, wherein the thermal conductivity ofsaid insulation plate is in the range of 0.05-0.5 kcal/m/hr./*K. 16.Apparatus as claimed in claim 2, wherein said insulation plate has acompression resistance in the range of 200-2,000 kg./cm.2 attemperatures between 180*-200*C.
 17. Apparatus as claimed in claim 2,wherein said insulation plate has a modulus of elasticity of at least1.5 X 105 kg./cm.2.
 18. Apparatus as claimed in claim 2, wherein saidinsulation plate is constituted of an asbestos fiber and thermoset resinmixture.
 19. Apparatus as claimed in claim 18, wherein said thermosetresin comprises phenol resin.
 20. Apparatus as claimed in claim 2,wherein said insulation plate includes, on the side face thereof whichconfronts and contacts said mold, aa thin layer of hardenable, flexiblematerial which undergoes increasing hardening when subjected to the heatand pressure of said heated mold, said layer having on the surfacethereof facing said mold a profile complementary to the profile of thesurface of said mold in contact therewith.
 21. Apparatus as claimed inclaim 20, wherein said thin layer is constituted of an asbestos fiberand thermoset resin mixture.
 22. Apparatus as claimed in claim 21,wherein said thermoset resin of said thin layer comprises phenol resin.23. Apparatus as claimed in claim 2, wherein said insulation plate has athickness sufficient to maintain a temperature gradient thereacross suchthat, when the side face thereof which confronts said mold is at thecuring temperature for said elastomeric stock in said mold cavities, thetemperature on the opposite side face of said insulation plate whichconfronts said chamber remains at a temperature insufficient to causethe excess elastomeric stock remaining in said chamber to become cured.24. Apparatus as claimed in claim 2, including respective annular insetsdisposed in said apertures of said insulation plate, said annular insetsbeing constituted of a material having an adhesion resistance to saidelastomeric stock greater than that of said insulation plate. 25.Apparatus as claimed in claim 24, wherein said annular insets areconstituted at least in part of polytetrafluoroethylene or a likematerial.
 26. Apparatus for molding elastomeric stock, said apparatuscomprising: a heated mold provided with a plurality of mold cavities forshaping and curing elastomeric stock in the form of said cavities; anelastomeric stock injection unit having a chamber in which elastomericstock is disposable and can be subjected to pressure for transfer fromsaid chamber; a multi-apertured, heat-resistant, flexible insulationplate carried by sAid injection unit at an end of said chamber, theapertures of said plate communicating with corresponding ones of saidmold cavities; a correspondingly multi-apertured, flexible linersuperposed along and affixed to one side face of said plate andconfronting said mold, said liner having pre-formed profileirregularities, along the surface thereof which confronts and forms aparting line with said mold, which are complimentary to and underpressure flexibly intermesh with profile irregularities of theconfronting surface of said mold; and means for moving said mold andinjection unit relative to one another such that said confrontingsurface of said mold is pressed against said liner and saidcomplimentary profile irregularities of each sealingly intermesh withone another; whereby, without separation of said mold and injectionunit, upon exertion of pressure in said chamber against said stock aportion of the latter will be expelled from said chamber and transferredthrough the apertures in said plate and liner into said mold cavitieswithout seepage of elastomeric stock at the parting line between saidmold and liner and without curing of elastomeric stock in said injectionunit curing curing of elastomeric stock in said mold cavities. 27.Apparatus as claimed in claim 26, including means for heating said mold,said plate being made of thermal insulatory material.
 28. Apparatus asclaimed in claim 27, wherein said liner and said plate are eachconstituted of an asbestos fiber and thermoset resin mixture.